This invention relates to a method of reforming soft ground, accumulated sludge layer and the like to provide a solid foundation therein.
Great difficulties are encountered when reclaiming land from the sea or building a bank or other structures on a layer of soft soil accumulated on the seabed or on land. For instance, the soft soil layer on the seabed is, in most cases, unable to sustain the load of the structure or earth laid thereon because unconfined compression strength of such soil is usually as low as around 0.1 Kg/cm.sup.2.
Therefore, in order to make such land reclamation or build a structure on soft ground, it is necessary to strengthen the ground by performing a consolidation treatment on the soft soil layer or by other means.
Among the conventional methods for the purposes mentioned above are the followings;
1. Displacement method in which the soft soil is replaced with sand,
2. Method in which sand piles or drains are constructed the soft ground to increase the degree of consolidation of soil,
3. Sand compaction method.
The aforementioned three are physical reforming methods and another is chemical one.
4. Chemical reforming methods in which earth is consolidated by using quicklime or liquid chemicals.
Any of these known methods, however, was unsatisfactory in some respects. For example, the above method (1) requires a vast volume of sand or soil to be wasted and then involves the difficult problem of disposal of the removed soft soil, while the methods (2) and (3), in addition to the above mentioned problem, require a long term of works and also their effect is uncertain. These methods (2) and (3) have the tendency of settlement of the reclaimed land or structures built on the reformed ground after the work.
According to the method (4), the soft soil is agitated with the chemical hardener by an agitator to mix and knead them up. This method is divided into two types, one in which the soft soil is treated in its entirety at the site, while the other in which it is treated portionwise by a unit volume of soil at one time. The former type requires much time and labor and hence is expensive. Also, the soft soil is treated at the site (in the accumulated form) in said both types of method, then it is difficult to obtain the reformed ground with uniform strength, because the soft layer such as the sludge layer formed as a result of long-year accumulation of various kinds of substances may include the layer or layers of hardly solidifiable soil such as corroded soil, and also because the various layers may not be constant in water content. It is, moreover, difficult to examine and confirm the existence of such layers and water contents thereof prior to the work. For these reasons, it was hardly possible to obtain solid ground with uniform strength through these conventional methods and to design the structural foundation by utilizing the treated ground as solid foundation for buildings. Also, in case that the soft ground partly includes a hardly solidifiable soil layer or layers, there arise the problems of settlement, heaving or landslide to be unable to expect desired effects of reformation. Further, these conventional methods include the problems of low efficiency of agitation or a lot of consumption of the chemical hardener.